The proposed research will investigate a number of transport phenomena associated with blood platelets. The first of these is the movement of 5-hydroxytryptamine across the platelet plasma membrane. Studies on the mechanism of this transport process will be continued, and the isolation of membrane component(s) responsible for transport will be attempted. Transport and storage of 5-hydroxytryptamine by intracellular platelet storage organelles will be examined to determine how this system differs from 5-hydroxytryptamine transport by plasma membrane, and what mechanism is involved in the apparent accumulation of 5-hydroxytryptamine against its concentration gradient. The third major area of investigation will be to determine the initial responses of the platelet plasma membrane to aggregating agents, to the extent that these responses affect membrane transport parameters.